1. Field of the Invention
This invention relates to a primary or secondary (backup) system for actuating a submerged hydraulic system. Specifically, the invention pertains to a primary system for actuating submerged fluid-actuable equipment. Also it pertains to a secondary power system to backup a primary one that has temporarily failed so that the fluid actuatable equipment is still operatable.
2. Prior Art
Subsea systems (powered by electric, hydraulic or pneumatic power) can be used for many purposes. They may, for example, control subsea tank valves or subsea wellheads.
By way of example, we will explain the use of this invention with a "blowout preventer (BOP) stack" used in drilling wells on the ocean floor. The BOP provides means for closing a well head either fully or around a drill pipe to contain well pressure or circulate, condition and return fluids to and from a subsea oil well so as to maintain well pressure control. On occasion its primary power system may fail to provide power to operate the BOP stack.
The current procedure used in case of such a failure utilizes a diver-connected power source instead of devices that are actuated by apparatus which utilize the ambient pressure in which the system is submerged. This procedure is time-consuming, and at depths over several hundred feet may be impossible to accomplish without a submarine vessel. One alternate approach, which is likewise time-consuming, is to lower an energizing hydraulic spear (attached to hydraulic lines) down into a receptacle on the BOP stack. The receptacle is hydraulically connected to actuators that operate selected functions of the BOP stack. If this is not possible, control of the subsea system may be lost or at least required to be temporarily abandoned.
Noteworthy is that failure of the source of power becomes less probable when the method and apparatus of this invention is used as the primary power source. The reason is that it does not rely entirely on the operation of a hydraulically or electrically powered system. Further, the negative energy supply system is a quick-response one, since it is located adjacent to the equipment it operates. Contrasted to this is a hydraulic system which has a source of fluid located at the water surface such as on a drilling platform. The response of such a system to operate deeply submerged equipment is considerably slower than the present invention because of the long distance the fluid must travel.